1. Field of the Invention
This invention relates to an improved form of a system for automatic positioning of a mirror mounted on a towing vehicle for effective rear vision at different angles between the towing vehicle and a towed vehicle. More particularly, it relates to such a system which is easily installed on a variety of towing and towed vehicle configurations and which is capable of properly positioning the mirror automatically under a variety of vehicle operating conditions. Most especially, it relates to such a system that may be easily installed on existing equipment without extensive modification to accept the system.
2. Description of the Prior Art
A right rear view mirror mounted outside of a tractor cab is usually positioned so that, as the driver looks out the right window, his line of reflected sight is directed toward the right rear edge of a trailer being pulled by the tractor. When the tractor is turned relative to the trailer, this direct line of sight is lost. The left mirror is affected in a similar way.
Most mirrors are constructed with a width of about 6 to 7 inches, giving the driver a view of an area including a region slightly forward of the rear edge of the trailer and slightly beyond the rear edge, so that the driver will have a fairly wide view of vehicles traveling behind the tractor.
When the driver negotiates a right turn of 45 degrees, the driver's line of sight is directed by the mirror to a point well forward of the right rear end of the trailer. For a 45 degree turn, this line of sight is very near the front of the trailer. For the driver to see the usual region near the rear of the trailer, the mirror needs to be rotated in a counterclockwise direction. The extent of rotation for different turns varies on the basis of turn angle, trailer length, trailer combinations, axle positions, and similar variables.
A good view of the vehicle rear is often important. When backing into a loading or unloading area, such as a dock, the tractor is almost always at some angle relative to the trailer for the docking maneuver. The backing maneuver must be fairly accurate, both in the distance from the dock and the lateral position of the trailer adjacent to the material to be loaded or a particular door in a warehouse. At any angle of the tractor to the trailer, the driver should be able to see the trailer rear well to position the trailer as required. Since the rear view mirrors on tractors are presently stationary, it is often necessary for the driver to leave the vehicle, get additional assistance to perform the parking maneuver, and/or use trial and error in several attempts. Such maneuvering may result in damage to the vehicle, the dock, or parked vehicles.
The docking procedure is one of the most difficult for the beginning driver to learn. It takes considerable time for the driver to learn the necessary "feel" for his location relative to the dock when it is not in the line of sight. Also, this "feel" will change from one tractor-trailer to another.
Rearward vision at different tractor-trailer angles is also important when the tractor-trailer must negotiate a turn on a narrow street or other confined area due to parked cars or traffic. When a tractor-trailer turns a corner too sharply, the rear trailer wheels will often pass over the street curb. Such turns can be properly carried out with good rear vision. Passing the rear wheels over the curb is dangerous for a number of reasons, including pedestrian injury or apprehension, tire damage and load damage.
A variety of systems for rotating the rear view mirrors to improve rear vision have been proposed. These systems use mechanical, electrical or combined mechanical and electrical means to rotate the rear view mirror remotely from inside the vehicle, either automatically or under driver control. None of the prior art automatic approaches have been successful and/or have serious shortcomings. Such systems are disclosed in the following issued U.S. patents:
U.S. Pat. No. 3,761,164, issued Sept. 25, 1973 to McKee et al., discloses an automatic mirror rotation system comprising a mechanical linkage attached between the steering linkage of a tractor and the rear view mirror. This mechanism does not take the relative position of the tractor and the trailer into consideration.
U.S. Pat. No. 3,749,480, issued July 31, 1973 to De Witt et al., discloses a system incorporating a mechanical sensing device adjacent the "fifth wheel" to sense relative motion between a tractor and trailer and analog electrical circuitry connected to rotate the rear view mirror on the basis of sensor inputs. This patent contains an extensive discussion of the tradeoffs of different measuring points for relative movement between the tractor and the trailer, including the steering column. While this system is capable of handling variation in the location of the rear wheels of the trailer, it is not sufficiently flexible to handle the wide variations encountered with different rigs that may be attached to a tractor in commercial hauling. The linkage connected to position the mirror is also cumbersome and prone to damage.
U.S. Pat. No. 3,469,901, issued Sept. 30, 1969 to Cook et al., discloses a system in which a plurality of switch contacts are located adjacent to the "fifth wheel" for operating a coil in a three coil relay. Energization of each coil progressively rotates the rear view mirror a given number of degrees. This system requires each trailer to be modified to provide contacts mounted on the trailer underside to cooperate with contacts adjacent the "fifth wheel". Attachment of the tractor to different trailers and maintenance are difficult. This system is useful only with specially modified trailers.
U.S. Pat. No. 2,988,957, issued June 20, 1961 to Kotora, discloses a system with a rear view mirror adjustment which operates from the steering column. This device operates on the turning of the wheels alone and has no relation to the angle of a towed vehicle.
U.S. Pat. No. 2,854,892, issued Oct. 7, 1958 to Stark provides a rear view mirror assembly for a tractor-trailer in which the adjustment of the mirror is accomplished by a linkage to the wheels. This device is difficult to attach, adjust, and reach. As in the case of the other systems tied to steering, it is not necessarily desirable to have the rear view mirror turn each time the wheels turn. The desire is to have the device function relative to the trailer, not just one wheel of the tractor.
The following additional issued U.S. patents disclose various mechanical mirror rotating systems: U.S. Pat. No. 3,950,080, issued Apr. 13, 1976 to McKee et al.; U.S. Pat. No. 3,741,633, issued June 26, 1973 to Haley; U.S. Pat. Nos. 3,640,609 and 3,640,608, both issued Feb. 8, 1972 to McKee et al., U.S. Pat. No. 3,476,464, issued Nov. 4, 1969 to Clark; U.S. Pat. No. 3,208,343, issued Sept. 28, 1965 to Prochnow; U.S. Pat. No. 3,166,630, issued Jan. 19, 1965 to Esslinger.
Thus, while the art pertaining to such mirror positioning systems is a well developed one, no prior art device has been successful because the mechanical linkage systems of such devices are too costly, too difficult to install, and too difficult to adjust for varying circumstances, such as different size trailers, combinations of trailers, and movable axles on tractors and trailers.